The present invention relates to a toner and an image forming method.
When toner images are fixed utilizing a heated roll fixing system, heretofore, it has been known that as a means to minimize the generation of offset phenomena, silicone oil is applied to the surface of said heating roller in a fixing unit so that said heating roller is treated for releasability for toners. Such a method is advantageous, since types of used toners are not limited.
In such a method, however, the silicone oil, which is applied to the surface of the heating roller for an extended period of time, is modified (or gelled) to result in offsetting due to a decrease in releasability provided with said roll, and during image formation, image staining occurs. As a result, the working life of the fixing unit is shorter compared to one to which silicone oil is not applied.
Further, there is another problem in which volatile components in the silicone oil, volatilize due to heat on the surface of the heating roller, and adhere to and stain the optical system, charging electrodes, and the like, resulting in image problems.
From the viewpoint of the foregoing, it has been demanded that no silicone oil be applied to a fixing unit (specifically, a heating roller), or only a very small amount of silicone oil be applied to the fixing unit.
In order to respond to such a demand, it has been common practice for a toner itself to be provided with releasability by adding releasing agents to said toner.
In such cases, in order to allow a toner to exhibit, to the greatest extent, the effects of the addition of releasing agents, it is required that said releasing agent in said toner exists in a domain state. In order to realize said state, generally, said releasing agents are not compatible with binder resins constituting said toner.
Conventionally, a toner, comprised of binder resins, colorants, and releasing agents, is produced employing a method (hereinafter referred to as a xe2x80x9ckneading and pulverization methodxe2x80x9d) in which said binder resins, said colorants, and said releasing agents are melt kneaded, and then pulverized, and if desired, classified.
In said kneading and pulverization method, a toner is prepared by dispersing releasing agents, which are insoluble in the binder resins, into said binders, and subsequently pulverizing the resultant dispersion. As a result, the resultant toner particles tend to result in non-uniformity and fluctuation of the dispersed state of releasing agents (in terms of the dispersed region, as well as the dispersed amount) and of the surface state.
When a toner, comprised of said non-uniform particles, is employed in image formation over an extended period of time, tiny offset-resulting components are adhered to the heating roller, and accumulate onto the surface of said heating roller and/or the pressure roller to result in image problems.
Such problems tend to occur due to effects of the generation of offsetting on the high temperature side heated by excessive fixing heat during high speed fixing, and by accumulated heat at the edges of the roller during switching of transfer sheets from a small size to a large size.
From the view of the foregoing, the present invention has been achieved.
An object of the present invention is to provide a toner which is employed in an image forming method comprising a process for forming fixed images, employing a fixing unit to which no silicone oil is applied, or only a very small amount of silicone oil is applied, and is capable of forming excellent images without resulting in image staining as well as image problems for an extended period of time, and further is capable of extending the working life of said fixing unit.
The invention and its preferable embodiment are described.
An image forming method comprising developing an electrostatic latent image formed on a photoreceptor to form a toner image employing a developer comprising a toner, transferring the toner image onto an image forming material, and fixing the transferred toner image employing a fixing unit, wherein
the fixing unit comprises a heating roller and a pressure roller which is brought into contact with said heating roller,
the heating roller comprises a cylinder having an interior diameter of from 10 to 70 mm and a wall thickness of from 0.1 to 2 mm comprised of a metal or a metal alloy, and a heating member being incorporated in the interior, a surface of the cylinder being covered with a layer comprising a fluorine resin at a thickness of from 10 to 500 xcexcm,
the pressure roller comprises a metal cylinder covered with a covering layer comprising an elastic material having an Asker hardness C of less than 80 degrees at a thickness of 0.1 to 30 mm, and
the toner comprises at least of a binder resin, a colorant, and a releasing agent, and is obtained by salting out/fusing resin particles comprising the releasing agent in binding resin and colorant particles.
The preferable fluorine resin is polytetrafluoroethylene or tertafluoroethylene-perfluoroalkyl vinyl ether copolymer.
The cylinder of the heating roller is preferably composed of iron, aluminum, copper, or alloy thereof.
The elastic material is soft rubber or foamed rubber, and more preferably urethane rubber, silicone rubber, or silicone sponge rubber.
The most preferably example of the elastic material is silicone rubber, or silicone sponge rubber.
The Asker C hardness of elastic material is preferably less than 70 degrees.
The Asker C hardness of elastic material is preferably less than 60 degrees.
In the image forming method the preferable example of the releasing agent is represented by Formula (1),
R1xe2x80x94(OCOxe2x80x94R2)nxe2x80x83xe2x80x83(1) 
wherein R1 and R2 each represent a hydrocarbon group having from 1 to 40 carbon atoms which may have a substituent, and n represents an integer of 1 to 4.
In the image forming method silicone oil is supplied to the heating roller in amount of, preferably, not more than 2 mg per A4 sized sheet of paper.
The thickness of the layer comprising the fluorine resin is preferably 20 to 400 xcexcm.
The thickness of the covering layer is preferably 0.1 to 20 xcexcm.
The temperature of fixing is preferably 150 to 210xc2x0 C.
The content ratio of releasing agents in the toner is preferably 1 to 30 percent by weight.
The toner has an average value preferably of the shape coefficient of 0.930 to 0.980.
The toner of the present invention is employed in an image forming method which comprises processes in which an electrostatic latent image, formed on a photoreceptor, is developed employing a developer comprising said toner, subsequently the formed toner image is transferred onto a support, and the transferred toner image is then fixed employing a fixing unit. Said fixing unit is comprised of a heating roller and a pressure roller which is brought into contact with said heating roller. Said heating roller is constituted in such a manner that the surface of a cylinder having an interior diameter of 10 to 70 mm and a wall thickness of 0.1 to 2 mm, comprised of a metal or a metal alloy, is covered with fluorine resins at a thickness of 10 to 500 xcexcm and a heating member is incorporated in the interior. Said pressure roller is constituted in such a manner that the surface of a metal cylinder is covered with an elastic material having an Asker hardness C of less than 80 degrees at a thickness of 0.1 to 30 mm. Said toner is comprised at least of a binder resin, a colorant, and a releasing agent, and is obtained by salting out/fusing resin particles comprising releasing agents in binding resins and colorant particles.
When the toner of the present invention is employed, the supply amount of silicone oil to said heating roller comprised of said fixing unit is preferably not more than 2 mg/A4 sized sheet of paper.